1. Field of the Invention
The present invention is directed to an x-ray radiator of the type having a housing containing a fluid coolant wherein a rotating bulb tube is rotatably mounted, the rotating bulb tube having an evacuated vacuum housing containing a cathode and an anode, the anode forming a wall of the vacuum housing being charged at its exterior by the coolant.
2. Description of the Prior Art
An x-ray radiator of the above type whose anode is directly cooled by the coolant is disclosed, for example, in U.S. Pat. No. 4,993,055. Such x-ray radiators basically allow the realization of extremely high x-ray powers but, in practice, present the problem of achieving the necessary heat transmission coefficients and the heat transmission from the exterior of the anode to the coolant in contact therewith.
The heat transmission from the exterior of the anode to the coolant can be improved by increasing the speed of the rotating bulb tube and/or the average radius of the anode, which approximately corresponds to the focal path radius. Both measures are possible only to a limited extent since enlarging the average radius of the anode is limited by the maximally allowed structural size of the x-ray radiator, and the frictional losses occurring between the rotating bulb tube and the coolant rapidly become unacceptably high with increasing speed of the rotating bulb tube, at least in the case of liquid coolants.
An object of the present invention is to provide an x-ray radiator of the type initially wherein an improvement of the heat transfer from the outside of the anode to the coolant is achieved without increasing the average radius of the anode and without increasing the rotational speed of the rotating bulb tube.
This object is inventively achieved in an x-ray radiator having a housing containing a fluid coolant, i.e. gaseous or liquid coolant wherein a rotating bulb tube is rotatably mounted, the rotating bulb tube having an evacuated vacuum housing containing a cathode and an anode, the anode forming a wall of the vacuum housing and being charged by the coolant at its exterior and having a profiling that increases the surface area of the exterior. For example, the exterior can be roughened and/or provided with ribs and/or with at least one channel in preferred embodiments of the invention. As a result of such an enlargement of the surface area of the exterior of the anode by profiling, more heat per time unit can be transmitted from the exterior of the anode to the coolant at a given speed of the rotating bulb tube and given average diameter of the anode. Given a constant quantity of heat transmitted per time unit from the exterior of the anode to the coolant, alternatively, the average diameter of the anode and/or the speed of the rotating bulb tube can be reduced.
German Patent 718031 and German OS 23 50 807 disclose x-ray tubes with a stationary anode which is a hollow body and whose interior charged with a coolant, the interior being provided with a profiling that increases the surface thereof. The anode does not rotate relative to the coolant nor is the exterior of the anode charged by the coolant.
This is also true of an x-ray tube disclosed in U.S. Pat. No. 5,056,127 with a rotating anode. Here, too, the anode is as hollow body whose inside charged by a coolant is provided with a profiling that increases the surface thereof. The coolant is located in the rotating anode.
In a preferred embodiment of the invention the profiling is fashioned such that it develops a conveying effect for the coolant. In this case, thus, the profiling performs an additional function of promoting a flow of the coolant, for example in a coolant circulation path, so that a pump for maintaining such a circulation is either completely dispensable, or can exhibit reduced power.
In one version of the invention, an especially good conveying effect is achieved wherein the exterior of the anode is arranged adjacent to and opposite a transverse wall of the housing that has an opening penetrated by a bearing shaft serving for the rotatable bearing of the rotating bulb tube in the housing such that an inflow cross section for coolant remains, the coolant flowing from the housing in the region of the outer circumference of the anode. The spacing between the transverse wall and the outside of the anode that enables an optimum conveying effect is dependent on the selected type of profiling; this can be determined by a person skilled in the art on the basis of simple trials.
A good conveying effect is achieved when the profiling of the exterior of the anode is formed by at least one channel proceeding helically from the center of the anode toward its periphery.